In recent years, much work has been done to develop methods for effectively utilizing microbial cells as feeds, foodstuffs, medicines, industrial materials, etc. To produce microbial cells with industrial advantages, methanol is expected to be used as a major carbon source because there is a good prospect that methanol will be supplied in great quantities and at low costs by the chemical industry. [See, for example, Japanese Laid-Open Patent Publications Nos. 14389/1972 and 15490/1978.]